1. Field of the Invention
The present invention relates to an optical pickup apparatus which performs recording and/or reproduction by using light with multiple kinds of wavelengths.
2. Description of the Related Art
A structure shown in FIGS. 4A and 4B has been known as an embodiment of a conventional optical pickup apparatus. Note that FIG. 4A shows a side view of an optical system of the optical pickup apparatus, while FIG. 4B shows a plan view of the optical system of the optical pickup apparatus.
As shown in the drawings, an optical pickup apparatus 31 includes first and second light sources 32A and 32B configured to emit light beams, and first and second optical systems 34A and 34B configured to guide the emitted light beams to an optical disk 42 and to guide light beams reflected from the optical disk 42 to first and second light-receiving elements (PDIC) 33A and 33B.
Specifically, the first light source 32A emits a light beam for CD and DVD, while the second light source 32B emits a light beam for BD. The light beams respectively emitted from the first and second light sources 32A and 32B respectively travel on optical paths of the first and second optical systems 34A and 34B. The first and second optical systems 34A and 34B include first and second polarization beam splitters 35A and 35B, first and second collimator lenses 36A and 36B, a reflecting mirror 37, first and second quarter wavelength plates 38A and 38B, first and second objective lenses 39A and 39B, first and second HOE (Holographic Optical Element) 40A and 40B, first and second PDIC 33A and 33B, first and second front monitor diodes 41A and 41B, and the like (This technology is described, for instance, in Japanese Patent Application Publication No. 2009-32304, on pages 7 to 9 and FIGS. 1 and 2).
Moreover, for an optical pickup apparatus supporting various kinds of optical disks such as BD, DVD, and CD, a structure is known in which an optical path for BD and an optical path for DVD and CD are guided to a shared optical path. Specifically, reflecting mirrors are respectively disposed directly under an objective lens for BD and an objective lens for DVD and CD. Each of light beams corresponding to these kinds of optical disks is guided on the shared optical path and is reflected by the reflecting mirror to enter the objective lens for BD or the objective lens for DVD and CD (This technology is described, for instance, in Japanese Patent Application Publication No. 2008-204496, on Pages 7 to 9 and FIGS. 1 and 2).
As described above, in the conventional optical pickup apparatus 31, the light beam emitted from the first light source 32A passes through the optical path of the first optical system 34A and enters the optical disk 42. The light beam reflected by the optical disk 42 similarly passes through the optical path of the first optical system 34A and enters the first PDIC 33A. On the other hand, the light beam emitted from the second light source 32B passes through the optical path of the second optical system 34B and enters the optical disk 42. Similarly, the light beam reflected by the optical disk 42 passes through the optical path of the second optical system 34B and enters the second PDIC 33B.
That is to say, since the optical path of the first optical system 34A is different from the optical path of the second optical system 34B, the number of parts of the optical systems disposed inside the optical pickup apparatus 31 becomes larger. This causes a problem that a longer time is required for attaching the parts or adjusting optical axes. Specifically, the light beam emitted from the first light source 32A is reflected by a reflection surface of the reflecting mirror 37 on the left side of the sheet surface and, then, enters the first wavelength plate 38A. On the other hand, the light beam emitted from the second light source 32B is reflected by a reflection surface of the reflecting mirror 37 on the right side of the sheet surface and, then, enters the second wavelength plate 38B. As a result, since the optical paths of the first and second optical systems 34A and 34B to the reflecting mirror 37 are different from each other, each of the optical paths requires the attachment operation of the parts of the optical system and adjustment of the optical axes. Similarly, since the first and second wavelength plates 38A and 38B are separately disposed, attachment operation and adjustments of optical axes are required.
Also, since the optical systems 34A and 34B have different optical paths, parts of the optical systems are required for each of the optical systems 34A and 34B. Moreover, space for the optical paths has to be secured. This causes a problem that it is difficult to reduce the optical pickup apparatus 31 in size.
As described above, in an optical pickup apparatus in which reflecting mirrors are disposed directly under each of an objective lens for BD and an objective lens for DVD and CD, optical paths are shared, so that for example, a light beam for BD is transmitted through the reflecting mirror for DVD and CD, is reflected by the reflecting mirror for BD, and then enters the objective lens for BD. In addition, a reflection film is formed on the reflecting mirror for DVD and CD. The reflection film has a phase characteristic having a wavelength dependency with respect to the light beam for BD. With this structure, the light beam for BD generates a phase difference after transmitted through the reflecting mirror for DVD and CD. Thus, there is a problem that the light beam for BD is irradiated onto the optical disk in the form of an elliptically polarized light. Essentially, it is designed that the light beam is polarized to a circularly polarized light by the quarter wavelength plate and is irradiated onto the optical disk in the form of the circularly polarized light. Note that if the objective lens for BD and the objective lens for DVD and CD are disposed in reverse positions, the light beam for DVD and CD is transmitted through the reflecting mirror for BD. Thus, there is caused a problem that the light beams for DVD and CD similarly generate a phase difference and the light beam to be irradiated onto the optical disk becomes an elliptically polarized light.